1. Field of the Invention
The present invention relates to a brushless motor which rotates disks such as CD (Compact Disk), DVD (Digital Versatile Disc), and MD (Mini Disk).
2. Background of the Related Art
Conventionally, added to a brushless motor is a separation preventing structure to prevent separation of a rotor from a motor in case a force overtaking the magnetic attractive force between the rotor magnet and a stator core is applied to the motor due to shock, etc. Adopted in general as the separation preventing structure is a structure wherein an engaging section is installed on a bearing housing, a separation preventing member is installed on a rotor unit opposing the bearing housing, and the two are engaged (see JP H10-23702 for example).
Also, adopted is a structure such as that in which a groove is formed on a part of a shaft to allow a separation preventing member to be engaged to the groove.
Shown in FIG. 8 is the structure of the conventional brushless motor. In FIG. 8, reference character 21 is a rotor, 22 is a shaft, 25 is a separation preventing member, 23 is a bearing, 24 is a bearing housing, 26 is a connection section, and 27 is a stator core. The bearing housing 24 is made by the metal cutting and shaving process, and an engaging section 26 is installed on the end section. The separation preventing member 25 has elasticity. In assembling the brushless motor, as the shaft 22 is inserted into the bearing 23, the tip of the separation preventing member 25 makes contact with the engaging section 26, and as the shaft 22 is further inserted, it expands in the outer diameter direction of the engaging section 26 by the elasticity of the separation preventing member 25. As the shaft 22 is further inserted, at the point when the tip of the separation preventing member 25 has passed the outer diameter of the engaging section 26, it becomes smaller than the outer diameter of the engaging section 26 due to its elasticity. As a result, it returns to its original shape, and thus the tip of the separation preventing member 25 enters the engaging section 26 to function as a separation preventer.
With current disk drives, thickness reduction and miniaturization are demanded, and as the often used bearing retaining structure for a brushless motor, other than those using a metal cut/shaved member such as brass as a bearing housing which is a bearing retaining member as in the conventional brushless motor, various kinds are proposed, such as those using a sintered member of the same material as the bearing. In order to deal with the rapid cost reduction of recent years, it has become necessary to construct the bearing retaining structure with a combination of low-cost members.
Most representative is a structure in which the bearing retaining mechanism contains is only pressed metal items. As such structure several have been proposed.
In the case of the brushless motor shown in FIG. 13, the motor is constructed of a rotor unit 101 and a stator unit 102, a motor mounting plate 103 of the stator unit 102 has a burring section 104 formed around its central section by the burring process, which functions as a bearing housing by press fitting a bearing 106 which supports a shaft 105 in a freely rotatable manner within the burring section 104. At the entrance of the burring section 104, fixed by press fitting is a thrust cap 107 which supports the weight of the rotor unit 101 in the thrust direction. Indicated as 108 is an abrasion resistant thrust plate 108 (see JP H08-289523 for example).
In the case of a brushless motor shown in FIG. 14, the motor consists of a rotor unit 109 and a stator unit 110, a motor mounting plate 111 of the stator unit 110 has a burring section 112 formed around its central section by the burring process, and press fitted and fixed in the burring section is a cup-shape bearing housing 113 which has its bottom integrated with one end of the tube section. Fit inside the bearing housing 113 is a bearing 115 which supports a shaft 114 in a freely rotatable manner. Installed on the bottom section of the bearing housing 113 is an abrasion resistant thrust plate 116, by which the weight of the rotor 109 in the thrust direction is freely supported by this thrust plate 116 (see JP2000-125505 for example).
However, with the conventional construction shown in FIG. 8, there is the problem that, because the separation preventing member is difficult to operate from outside of the brushless motor, disassembly and repair after assembling are difficult. Also because the separation preventing member is installed in a very narrow space between the rotor and stator core, it is difficult to appropriately set the elasticity of the separation preventing member. Furthermore, since the separation preventing member is formed by press-processing a metallic plate, because it contains a bending process, it is difficult to maintain the bending angle with high accuracy.
The present invention solves such conventional problems, and has the objective of providing a brushless motor in which disassembly is easy, even after assembling, and adjusting the dimensions and setting the elasticity of the separation preventing member is also easy.
Also, in recent years, further miniaturization and thickness reduction are demanded to brushless motors used in disk drives.
However, in the conventional construction shown in FIG. 8, with the bearing retaining mechanism shown in FIG. 13, as the motor is made more compact and thinner, the length of the part where the bearing housing 24 is fixed to the motor mounting base becomes shorter in the press fit direction of the thrust cap 107 shown in FIG. 13, the joint strength decreases, and the retaining strength becomes short relative to the support of the weights of the rotor units 21 and 101 in the thrust direction. Even if an adhesive is used when fixing, the adhesive flows out to the parts of the bearings 21 and 106, negatively affecting reliability. Also, fixing by welding is difficult to implement due to its construction.
Also, in the bearing retaining mechanism shown in FIG. 14, as the motor is made more compact and thinner, the length of the bearing housing 113 and the motor mounting plate 111 in the press fit direction decreases, and the joint strength becomes short. With this construction, in order to take measures to support the weight of the rotor unit in the thrust direction as in the bearing retaining mechanism shown in FIG. 13, the outer diameter step section 117 of the bearing housing 113 must be supported by the end face of the burring section 118 of the motor mounting plate 111. If the motor is forcibly made compact and thinner, it becomes difficult to simultaneously securing both joint strength of the bearing housing 113 with the bearing 115 fit inside its inner diameter and joint strength with the motor mounting plate 111.
In the bearing retaining mechanism shown in FIG. 14 also, fixing is difficult to accomplish by welding due to its construction, similar to the case of FIG. 13, and fixing with an adhesive is not useful because there is concern that such adhesive might flow to the lower face of the motor mounting plate.
As the motor becomes more compact and thinner, it is obvious that securing the joint strength is accomplished only by press fit fixing, and the present invention has an objective of providing a brushless motor in which high supporting rigidity in the thrust direction weight of the rotor unit is secured, and in which the bearing housing can also have a highly-reliable tight connection other than by press fit fixing.